1. Field of the Invention
The present invention relates to integrated circuits, more particularly to capacitors with metal electrodes. The capacitors are used especially in memory cells of a memory plane.
2. Description of Related Art
The fabrication of capacitors is increasingly faced with problems associated with the high integration densities. This is because the increase in integration density means a reduction in the area of a memory cell, while still maintaining an effective capacitance. Thus, in current technologies, several approaches are possible.
The most common approach is the formation of the capacitor in a trench, allowing the area of the capacitor to be increased without increasing the area of the memory cell. The area may be further increased by a factor of about 2 by using, as lower electrode, doped polysilicon of the HSG (Hemispherical Grain) polysilicon type.
For even higher integration densities, there are several possible approaches that allow capacitors to be integrated into smaller and smaller cells.
The conventional approach consists in increasing the depth of the trench. However, this approach leads to form factors that cannot be easily controlled. Another approach consists in reducing the thickness of the dielectric, the risk being an increase in the leakage current.
Recent research has been carried out on the use of an insulator with a high dielectric constant and metal electrodes, making it possible to overcome the problems of doping three-dimensional polysilicon electrodes and to reduce the depletion capacitances associated with polysilicon electrodes. However, the conventional metal electrodes (for example made of TiN) are plane and their use therefore results in the factor of 2 provided by the use of a HSG polysilicon being lost.